The invention relates to an arrangement in the form of a portal positioned along a pathway for reading a transponder type device or tag attached to an object moving along the pathway through the portal. More particularly, the present invention relates to a portal reading arrangement for reading a preferably passive transponder type device or tag which is excited by an inductively coupled magnetic field of a first predetermined frequency to produce a magnetic and/or an electrostatic field of a second predetermined frequency modulated with a coded identifying signal which is inductively received and decoded by a receiver. Proximity type systems generally operating in this manner are disclosed for example in commonly owned U.S. Pat. No. 4,818,855 and copending allowed U.S. application 07/453,721, filed Dec. 18th, 1989 now U.S. Pat. No. 5,099727, the subject matter of which is incorporated herein by reference.
It is known to use systems of the above general type for the identification of objects moving along a pathway, for example, a conveyor belt or an animal walkway, for the purpose of identifying and/or controlling the movement of the object along the pathway as a result of the readout identification. In such systems, the transponder type device or tag is generally affixed to the object with a known orientation and position, and one or more readers are positioned along the pathway, for example above, below and/or to the side of the pathway, depending on the desired or known orientation of the tag on the object. While these systems operate satisfactorily when the orientation and/or position of the tag on the object is generally known, reading problems may occur if the tag is randomly oriented or randomly positioned. These reading problems may be caused for example because the tag has not been excited to produce an output signal, or because the output signal received by the receiving antenna is too weak. These problems generally occur because of the directional nature of the coupling mechanisms involved, and in particular the inductive magnetic field coupling used to excite the transponder or tag and/or to provide the received output signal. Additional reading problems can result due to the size, and thus the positioning of the tags relative to the readers, and/or due to the material from which the object is formed. For example, in the case of a metal object with a random orientation, the tag may be effectively shielded from the reading devices.
One type of pathway or conveyor system wherein automatic reading of tags affixed to objects moving along the conveyor would be most desirable is the baggage handling conveyor systems of the type commonly used, for example, by airlines at airports. As can easily be appreciated, the baggage or luggage transported by such conveyor systems is random in shape and material of construction, and is randomly oriented on the conveyor, often with little space between individual pieces of luggage. Thus, identifying tags fastened to the individual piece of luggage, for example tags indicating destination, flight or ownership, are likewise randomly oriented and positioned, thus rendering automatic reading of the tags most difficult.
At the present time identifying tags affixed to luggage in luggage conveying systems are either manually read or semimanually read by means of hand held optical scanners. Obviously, it would be desirable to provide an automatic system, and in particular a portal reader which could automatically read transponder type devices or tags containing the desired information irrespective of the orientation of the tags in such a baggage conveyor system. However, to be applicable, such a portal reader should be able to read the tags on the first try with a substantial degree of accuracy, e.g. close to 100% and the tags must be read in the same sequence as they appear on the conveyor. Additionally, the reader must be capable of reading the tags in all orientations, even if the tags disposed under the luggage, and should be capable of readings tags disposed on metal luggage, which tends to be most difficult in view of the shielding effect produced by the metal of the luggage.